Stylomecon G. Taylor

Elvebakk, Arve & Bjerke, Jarle W., 2024, Papaver recircumscribed: A review of neighbouring Papaveraceae genera, including Afropapaver nom. et stat. nov. and Oreomecon, a large, Arctic-Alpine genus, PhytoKeys 248, pp. 105-188 : 105-188

6. Stylomecon G. Taylor , J. Bot. 68: 140. 1930

Type species.

Stylomecon heterophylla (Benth.) G. Taylor.

Notes.

Stylomecon heterophylla (Benth.) G. Taylor and the species known as Papaver californicum A. Gray are endemic to California and adjacent parts of Mexico, where they are grossly disjunct as they are the only representatives of the mostly Eurasian clade of Papavereae in America. Samples from this group of species diverged from the remaining samples of Papaver and Parameconopsis at ca. 19–20 Ma according to the phylogenies by Valtueña et al. (2012) and Xie et al. (2014) and a similar phylogenetic position was shown by Liu et al. (2014). Catania et al. (2022) concluded that Papaver californicum was the earliest branching species from a common ancestor in the Papaver lineage, which had a gene fusion event basal for the further synthesis of the morphinan group of alkaloids, a divergence dated at 16.8 Ma.

According to these phylogenies, these two species definitively should be congeneric. Kadereit and Baldwin (2011) dealt with their morphology, ecology and distribution in detail and showed differences in flower and capsule morphology. They concluded that the style in S. heterophylla probably evolved independently from other lineages and a structure similar to the stigmatic disc of P. californicum and they treated both species within a broad definition of Papaver .

Given that these two Californian-Mexican species have an old evolutionary history, a similar phylogeny and distribution and a diverging style which probably evolved relatively recently within its lineage, the clade is best treated as a separate genus. The name Stylomecon is available and a new combination is needed for the species known as P. californicum .

Stylomecon heterophylla was briefly described as Meconopsis heterophylla Benth. by Bentham (1835), who also described Meconopsis crassifolia Benth. Both type specimens shown by JSTOR Global Plants (2023) carry the label information “ Nova California, 1833, Douglas’. According to Bentham (1835), David Douglas travelled from present-day Oregon to then Mexican California and carried out botany studies in the surroundings of Monterey during the years 1831 and 1832. Then he travelled to what is now named Hawaii and dispatched his plants by ship to England before he returned to Oregon. The year of the label should, therefore, refer to the year of the plants’ arrival in England and not the year of collecting. According to Brentham (1835), cultivation attempts failed and the plants preserved are, therefore, those collected by Douglas. Although classified as isotypes by JSTOR Global Plants (2023), below, we list these as holotypes in the absence of known duplicates.

Steudel (1841) included both Meconopsis heterophylla and Meconopsis crassifolia within a widely defined genus Stylophorum Nutt. , including two from California, two others from northern America, one from Europe and two from Nepal. In a flora of the San Francisco area, Greene (1894) accepted both names as species of Papaver together with P. californicum and P. lemmonii Greene. Much later, Kadereit (1988 a) and Kadereit and Baldwin (2011) accepted only Papaver californicum and Stylomecon heterophylla and did not present interpretations of the name Meconopsis crassifolia . Grey-Wilson (2014), however, considered the latter to be a synonym of the very different Stylophorum diphyllum (Michx.) Nutt. distributed on the opposite side of the North American continent, an interpretation followed by POWO (2023).

Kadereit and Baldwin (2011) explained and illustrated the leaves of Stylomecon heterophylla to be very different from those of Papaver californicum , the latter being strikingly heterophyllous. The holotypes of Meconopsis heterophylla and M. crassifolia illustrated by JSTOR Global Plants (2023) differ in the same way and also match the diagnoses by Bentham (1835). We conclude that Meconopsis crassifolia and Papaver californicum are synonyms and that the former holds priority.